A MapNode is the scene graph node that renders a Map. Whether you loaded your
map from an Earth File or created it using the API, you can access the Map and its
MapNode at runtime to make changes. If you did not explicitly create a MapNode
using the API, you will first need to get a reference to the MapNode to work with.
Use the static get function:

The Map contains ImageLayer and ElevationLayer objects.
These contain some properties that you can adjust at runtime.
For example, you can toggle a layer on or off or adjust an ImageLayer opacity using the API: